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122                                Stamping.

between the crank arms. Probably this piece had better be
swaged next (it may require another heat), the forging being
turned round, backward and forward, to produce a good result
(see E). The distance between the cranks should be now finished
very exactly, by knifing or other means. The ends remain. Here
it is necessary to first cut out the superfluous material by marking
off at F3 punching the hole o, and, while the crank is still hot,
cutting out the rectangle with a knife or cutter (see H). After-
wards the shaft is rounded by swaging (j). When this has been
done for both ends, and the shaft carefully measured, as well as
tested for axial straightness, straightening if necessary, the work
may be considered complete. In this form of crank (double-
webbed) the pair of webs are always forged solid in the manner
described, and the piece between taken out either by slotting or
turning in the lathe,

A.t this point we may as well consider one other form of crank,
which has many advantages. In Fig. 120, A is the shaft alluded
to, and is there shewn finished by turning in the lathe. It is con-
siderably stronger than the one previously described, on account
of the fact that the fibres follow the bend of the crank webs
(represented in dotted lines), while in the shaft of Fig, 119 these
fibres are cut through when the mid pieces are slotted out, which
must of course weaken the webs considerably. The only
objection to the form here shewn is that a great xridth is required
for the crank itself, and, as this cannot always be spared, the
crank has only been applied on portable or traction engines up to
the present Properly we might have described this in the space
devoted to the forge, for a larger hammer is required than
commonly occurs in the smithy. A bar of the best Yorkshire
iron, of sufficient diameter to torn down to finished size, is heated
and placed between the blocks B B, and these are made to
approach each other by blows from the hammer, at first gently,
and afterwards more strongly. Lastly, the shaft must be tested
for stxaightaess.

Stamping*—Where several articles are required exactly alike
in form and dimension they can often be forged more cheaply
by the use of stamping tools, The crank last described might
almost b€ termed an example of this kind of work, and the lever